Magnetoelastic Torque Sensor With Local Measurement Of Ambient Magnetic Field

ABSTRACT

A torque sensor including a shaft that receives an applied torque is disclosed. The shaft includes a magnetoelastic region that generates a non-negligible magnetic field responsive to the applied torque and one or more null regions that each generates a negligible magnetic field. The torque sensor includes a plurality of null region sensors proximal a null region that generate a null region magnetic field measure corresponding to a magnitude of an ambient magnetic field. The torque sensor includes a magnetoelastic region sensor proximal the magnetoelastic region that generates a magnetoelastic region magnetic field measure corresponding to the magnitude of the ambient magnetic field and a magnitude of the non-negligible magnetic field. The torque sensor includes a controller coupled to the null region sensors and the magnetoelastic region sensor that calculates a magnitude of the applied torque based on the null region magnetic field measures and the magnetoelastic region magnetic field measure.

TECHNICAL FIELD

The present disclosure relates generally to systems, sensors, and methods of measuring applied torque using magnetoelastic techniques.

BACKGROUND

Typical torque sensors have certain disadvantages. For example, the presence of an ambient magnetic field can adversely affect their accuracy. A need exists in the art for improved torque sensors that account for and reject disruptive ambient magnetic fields.

SUMMARY

A torque sensor is disclosed. The torque sensor includes a shaft that receives an applied torque. The shaft of the torque sensor includes a magnetoelastic region that generates a non-negligible magnetic field responsive to the applied torque and one or more null regions that each generates a negligible magnetic field. The torque sensor also includes a plurality of null region sensors and a magnetoelastic region sensor. Each null region sensor is proximal one of the one or more null regions and generates a null region magnetic field measure corresponding to a magnitude of an ambient magnetic field. The magnetoelastic region sensor is proximal the magnetoelastic region and generates a magnetoelastic region magnetic field measure corresponding to the magnitude of the ambient magnetic field and the non-negligible magnetic field. The torque sensor also includes a controller coupled to the plurality of null region sensors and the magnetoelastic region sensor that calculates a magnitude of the applied torque based on the null region magnetic field measures and the magnetoelastic region magnetic field measure.

A torque sensor is disclosed. The torque sensor includes a shaft that receives an applied torque. The shaft includes a first null region, a second null region, and a third null region that each generate a negligible magnetic field and a first magnetoelastic region and a second magnetoelastic region that each generate a non-negligible magnetic field responsive to the applied torque. The torque sensor also includes a first null region sensor, a second null region sensor, and a third null region sensor. The first null region sensor is proximal the first null region and generates a first null region magnetic field measure corresponding to a magnitude of an ambient magnetic field. The second null region sensor is proximal the second null region and generates a second null region magnetic field measure corresponding to the magnitude of the ambient magnetic field. The third null region sensor is proximal the third null region and generates a third null region magnetic field measure corresponding to the magnitude of the ambient magnetic field. The torque sensor also includes a first magnetoelastic region sensor and a second magnetoelastic region sensor. The first magnetoelastic region sensor is proximal the first magnetoelastic region and generates a first magnetoelastic region magnetic field measure corresponding to the magnitude of the ambient magnetic field and a magnitude of the non-negligible magnetic field generated by the first magnetoelastic region responsive to the applied torque. The second magnetoelastic region sensor is proximal the second magnetoelastic region and generates a second magnetoelastic region magnetic field measure corresponding to the magnitude of the ambient magnetic field and a magnitude of the non-negligible magnetic field generated by the second magnetoelastic region responsive to the applied torque. The torque sensor also includes a controller coupled to the first null region sensor, the second null region sensor, the third null region sensor, the first magnetoelastic region sensor, and the second magnetoelastic region sensor. The controller calculates a magnitude of the applied torque based on the first null region magnetic field measure, the second null region magnetic field measure, the third null region magnetic field measure, the first magnetoelastic region magnetic field measure, and the second magnetoelastic region magnetic field measure.

A method of calculating a magnitude of an applied torque using a torque sensor is disclosed. The torque sensor includes a shaft that includes one or more null regions that each generates a negligible magnetic field and a magnetoelastic region that generates a non-negligible magnetic field responsive to the applied torque. The torque sensor includes a plurality of null region sensors each proximal one of the one or more null regions and a magnetoelastic region sensor proximal the magnetoelastic region. The torque sensor includes a controller coupled to the plurality of null region sensors and the magnetoelastic region sensor. The method includes steps of receiving the applied torque with the shaft, generating the non-negligible magnetic field responsive to the applied torque with the magnetoelastic region, generating a null region magnetic field measure corresponding to an ambient magnetic field with each null region sensor, generating a magnetoelastic region magnetic field measure corresponding to the ambient magnetic field and the non-negligible magnetic field with the magnetoelastic region sensor, and calculating the applied torque based on the null region magnetic field measures and the magnetoelastic region magnetic field measure with the controller.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages of the present disclosure will be readily appreciated, as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

FIG. 1 provides a perspective view of a torque sensor.

FIG. 2 provides a diagrammatic view of the torque sensor.

FIG. 3 provides a diagrammatic view of the torque sensor with a first ambient magnetic field superimposed.

FIG. 4 provides a diagrammatic view of the torque sensor with a second ambient magnetic field superimposed.

FIGS. 5A and 5B provide a flow chart of a method of calculating a magnitude of an applied torque using a torque sensor.

FIG. 6A provides a graph of a magnitude of the first ambient magnetic field with respect to distance along a shaft of the torque sensor.

FIG. 6B provides a graph of a magnitude of the second ambient magnetic field with respect to distance along the shaft of the torque sensor.

FIGS. 7A-7F provide alternative instances of the torque sensor.

DETAILED DESCRIPTION

FIG. 1 illustrates one instance of a torque sensor 10 that calculates a magnitude of an applied torque 12. The torque sensor 10 may be utilized in suitable applications and for any suitable component or system where the applied torque 12 is measured. For example, the torque sensor 10 may be utilized in, but not limited to, vehicular systems, such as electric power steering systems.

Referring to the instance of FIG. 1 , the applied torque 12 having a magnitude τ is applied to a first end 16 of a shaft 14 of the torque sensor 10 about an axis A. However, the applied torque 12 may be applied to any section of the torque sensor 10 about the axis A. For example, the applied torque 12 may be applied to a second end 18 of the torque sensor 10 or at any point between the first and second ends 16, 18 of the torque sensor 10. Furthermore, the applied torque 12 may be applied to more than one section of the torque sensor 10. Additionally, the applied torque 12 may be applied in a clockwise or counterclockwise direction when viewed from the first end 16 of the torque sensor 10. Depending on the system that utilizes the torque sensor 10, the applied torque 12 may be applied in either or both directions.

Although the shaft 14, as shown in FIG. 1 , has a cylindrical configuration, the shaft 14 may have any suitable shape defining any suitable cross-sectional area (e.g. a square, a triangle, an oval, an octagon, etc.) that enables the torque sensor 10 to properly function. Additionally, in other instances, the shaft 14 may be hollow or solid. Furthermore, in some instances, the shaft 14 may be stationary and fixed at the first and second ends 16, 18 to a larger system, which enables application of the applied torque 12 to deform the shaft 14. In other instances, the shaft 14 may rotate upon application of the applied torque 12.

As shown in FIG. 1 , the shaft 14 may include a first magnetoelastic region 20 and a second magnetoelastic region 22. A region may be magnetoelastic if the region generates a magnetic field responsive to a mechanical force. For example, in the instance of FIG. 1 , the first magnetoelastic region 20 and the second magnetoelastic region 22 may be magnetized to generate a magnetic field responsive to the applied torque 12 being applied to the shaft 14. In some instances, the first and second magnetoelastic regions 20, 22 may be magnetized circumferentially and may be magnetized to carry a positive or negative polarity. In FIG. 1 , the first and second magnetoelastic regions 20, 22 are magnetized to have a positive polarity, as illustrated by upward pointing arrows.

As shown in FIG. 1 , the shaft 14 may include a first null region 24, a second null region 26, and a third null region 28. The first, second, and third null regions 24, 26, 28 each generate a negligible magnetic field when no torque is applied to the shaft 14 and when the applied torque 12 is applied to the shaft 14. In other words, the magnetic field generated by the first, second, and third null regions 24, 26, 28 may be minimal when compared to the magnetic field generated by the first and second magnetoelastic regions 20, 22 and/or may be treated as negligible when determining the applied torque 12. As shown, the first, second, and third null regions 24, 26, 28 may carry a negligible magnetic polarization and are each illustrated in FIG. 1 using a null symbol (Ø). The first, second, and third null regions 24, 26, 28 and labelled Ø₁, Ø₂, Ø₃, respectively. This quality of the first, second, and third null regions 24, 26, 28 may be a manufactured, designed, or intrinsic quality.

FIG. 2 illustrates another view of the torque sensor 10, wherein relevant locations and lengths along the shaft 14 are labeled. As shown in FIG. 2 , the first magnetoelastic region 20 may be bound by a first end 30 and a second end 32. The second magnetoelastic region 22 may be bound by a first end 34 and a second end 36. The first null region 24 may be bound by a first end 38 and a second end 40, the second null region 26 may be bound by a first end 42 and a second end 44, and the third null region 28 may be bound by a first end 46 and a second end 48. In FIG. 2 , the first magnetoelastic region 20 is disposed between the first null region 24 and the second null region 26 such that the first end 30 of the first magnetoelastic region 20 contacts the second end 40 of the first null region 24 and the second end 32 of the first magnetoelastic region 20 contacts the first end 42 of the second null region 26. Additionally, the second magnetoelastic region 22 is disposed between the second null region 26 and the third null region 28 such that the first end 34 of the second magnetoelastic region 22 contacts the second end 44 of the second null region 26 and the second end 36 of the second magnetoelastic region 22 contacts the first end 46 of the third null region 28. FIG. 2 also notes a length of each region 20, 22, 24, 26, 28. Specifically, L_(M1) represents a length of the first magnetoelastic region 20. L_(M2) represents a length of the second magnetoelastic region 22, L_(N1) represents a length of the first null region 24, L_(N2) represents a length of the second null region 26, and L_(N3) represents a length of the third null region 28. It is to be appreciated that the ends of the regions 20, 22, 24, 26, 28 may be seamlessly integrated into the shaft 14 by virtue of magnetization and without demarcations shown in FIG. 2 .

FIG. 3 illustrates yet another view of the torque sensor 10, wherein magnetic fields generated by the first magnetoelastic region 20 and the second magnetoelastic region 22 are shown. As shown, the first magnetoelastic region 20 may generate a first non-negligible magnetic field 50 and the second magnetoelastic region 22 may generate a second non-negligible magnetic field 52. The first non-negligible magnetic field 50 and the second non-negligible magnetic field 52 will be referred to as the first magnetic field 50 and the second magnetic field 52, respectively, herein. As previously stated, the first, second, and third null regions 24, 26, 28 generate a negligible magnetic field. As such, in FIG. 3 , the first, second, and third null regions 24, 26, 28 are illustrated as generating no magnetic field.

When the applied torque 12 is applied to the shaft 14, the first magnetoelastic region 20 generates the first magnetic field 50 with a magnitude corresponding to the magnitude of the applied torque 12 and the second magnetoelastic region 22 generates the second magnetic field 52 with a magnitude corresponding to the magnitude of the applied torque 12.

Furthermore, the torque sensor 10 may be disposed within an ambient magnetic field 76, illustrated in FIGS. 3 and 4 using multiple dot-dashed lines and labeled B_(a). The ambient magnetic field 76 may be a magnetic field generated by sources external to the torque sensor 10. For example, in an instance where the torque sensor 10 may be utilized by an electric power steering unit, the ambient magnetic field 76 may be a magnetic field generated by components of the electric power steering unit not including the torque sensor 10. Furthermore, the ambient magnetic field 76 may be uniform or non-uniform. For example, in FIG. 3 , the ambient magnetic field 76 is a uniform ambient magnetic field. In FIG. 4 , the ambient magnetic field 76 is a non-uniform ambient magnetic field. The applied torque 12 has a minimal effect on the ambient magnetic field 76 as the ambient magnetic field 76 is generated by sources external to the torque sensor 10.

It should be noted that, at a point within the ambient magnetic field 76, the first magnetic field 50, and/or the second magnetic field 52, a magnetic field vector may be used to indicate a magnitude and a direction of magnetic forces at the point. For example, in FIG. 3 , the magnetic field vector 54 indicates a magnitude and a direction of a sum of the first magnetic field 50 and the ambient magnetic field 76 at point A. As another example, in FIG. 3 , the magnetic field vector 56 indicates a magnitude and a direction of a sum of the second magnetic field 52 and the ambient magnetic field 76 at point B. Furthermore, the magnetic field vectors may be composed of an axial magnetic field component and an orthogonal, radial magnetic field component (the axial and radial magnetic field components are named in relation to the shaft 14). For instance, the magnetic field vector 54 in FIG. 3 is composed of an axial magnetic field component 58 and a radial magnetic field component 60. Similarly, the magnetic field vector 56 is composed of an axial magnetic field component 62 and a radial magnetic field component 64.

Referring to FIG. 1 , the torque sensor 10 may also include magnetoelastic region sensors 66, 68 and null region sensors 70, 72, 74. Specifically, as shown in FIG. 1 , a first magnetoelastic region sensor 66 may be disposed proximal the first magnetoelastic region 20 and a second magnetoelastic region sensor 68 may be disposed proximal the second magnetoelastic region 22. Also shown in FIG. 1 , a first null region sensor 70 may be disposed proximal the first null region 24, a second null region sensor 72 may be disposed proximal the second null region 26, and a third null region sensor 74 may be disposed proximal the third null region 28.

It should be noted that the sensors 66, 68, 70, 72, 74 may be disposed proximal the regions 20, 22, 24, 26, 28 and need not be directly connected to the shaft 14. For example, in one instance, the sensors 66, 68, 70, 72, 74 may be disposed in a housing that may be adjacent to, but spaced from, the shaft 14. As such, the sensors 66, 68, 70, 72, 74 and the housing do not influence the applied torque 12 or the shaft 14 through friction.

Locations of the sensors 66, 68, 70, 72, 74 may correspond to distances along the shaft 14. In the instance of FIG. 2 , the sensors 66, 68, 70, 72, 74 are disposed at marked distances −s₂, −s₁, 0, s₁, s₂ along the shaft 14. The marked distances −s₂, −s₁, 0, s₁, s₂ are marked with respect to a Cartesian plane, with a location of the second null region sensor 72 corresponding to the origin of the Cartesian plane. As such, the first magnetoelastic region sensor 66 is disposed at −s₁ and the second magnetoelastic region sensor 68 is disposed at s₁. The first, second, and third null region sensors 70, 72, 74 are disposed at −s₂, 0, and s₂, respectively.

Further, it should be noted that, while the null region sensors 70, 72, 74 are illustrated as being smaller in size than the magnetoelastic region sensors 66, 68, the sensors 66, 68, 70, 72, 74 may be any suitable size. In some instances, the null region sensors 70, 72, 74 may be a same size as the magnetoelastic region sensors 66, 68. In other instances, the null region sensors 70, 72, 74 may be a greater or smaller size than the magnetoelastic region sensors 66, 68. Additionally, a size of the sensors 66, 68, 70, 72, 74 need not correspond to a length of the regions 20, 22, 24, 26, 28 to which the sensors 66, 68, 70, 72, 74 are proximally disposed.

Referring to FIG. 3 , the first magnetoelastic region sensor 66 may sense the first magnetic field 50 generated by the first magnetoelastic region 20 and the second magnetoelastic region sensor 68 may sense the second magnetic field 52 generated by the second magnetoelastic region 22. In other words, the first magnetoelastic region sensor 66 may generate a first magnetoelastic region magnetic field measure corresponding to a magnitude of the first magnetic field 50 and the second magnetoelastic region sensor 68 may generate a second magnetoelastic region magnetic field measure corresponding to a magnitude of the second magnetic field 52. The first and second magnetoelastic region magnetic field measures may correspond to a magnitude of the first and second magnetic field 50, 52, respectively. For example, in FIG. 3 , the first magnetoelastic region magnetic field measure may correspond to a magnitude of the first magnetic field 50 at point C and the second magnetoelastic region magnetic field measure may correspond to a magnitude of the second magnetic field 52 at point D. In some instances, the first and second magnetoelastic region magnetic field measures may correspond to a magnitude of an axial magnetic field component or a magnitude of a radial magnetic field component of the respective magnetic field.

Also shown in FIG. 3 , the first and second magnetoelastic region sensors 66, 68 may also sense a magnitude of the ambient magnetic field 76. Therefore, the first and second magnetic field measures generated by the first and second magnetoelastic region sensors 66, 68, respectively, may also correspond to the magnitude of the ambient magnetic field 76. For example, in FIG. 3 , the first magnetoelastic region magnetic field measure may correspond to the magnitude of the first magnetic field 50 and a magnitude of the ambient magnetic field 76 at point C and the second magnetoelastic region magnetic field measure may correspond to the magnitude of the second magnetic field 52 and a magnitude of the ambient magnetic field 76 at point D. As such, the first magnetic field measure may correspond to a magnitude of a sum of the ambient magnetic field 76 and the first magnetic field 50 and the second magnetic field measure may correspond to a magnitude of a sum of the ambient magnetic field 76 and the second magnetic field 52. In some instances, the first and second magnetoelastic region magnetic field measures may correspond to a magnitude of an axial magnetic field component or a magnitude of a radial magnetic field component of a sum of the ambient magnetic field 76 and the respective magnetic field.

Also shown in FIG. 3 , the first, second, and third null region sensors 70, 72, 74 may also sense the magnitude of the ambient magnetic field 76. In other words, the first, second, and third null region sensors 70, 72, 74 may generate a first, second, and third null region magnetic field measure, respectively, corresponding to a magnitude of the ambient magnetic field 76. The first, second, and third null region magnetic field measure may correspond to a magnitude of the ambient magnetic field 76. For example, in FIG. 3 , the first null region magnetic field measure may correspond to a magnitude of the ambient magnetic field 76 at point E, the second null region magnetic field measure may correspond to a magnitude of the ambient magnetic field 76 at point F, and the third null region magnetic field measure may correspond to a magnitude of the ambient magnetic field 76 at point G. In some instances, first, second, and third null region magnetic field measures may correspond to a magnitude of an axial magnetic field component or a magnitude of a radial magnetic field component of the ambient magnetic field 76.

It should be noted that the sensors 66, 68, 70, 72, 74 each may include a plurality of sensors. For example, in one instance, the first magnetoelastic region sensor 66 may include a plurality of sensors adjacent to the first magnetoelastic region 20 to generate the first magnetoelastic region magnetic field measure. In such an instance, the plurality of sensors may each generate a measure of the first magnetic field 50 and the ambient magnetic field 76 and the sensor 66 may average or filter the measures generated by each sensor of the plurality of sensors to generate the first magnetoelastic region magnetic field measure.

It should also be noted that the sensors 66, 68, 70, 72, 74 may be any sensor suitable for sensing a magnetic field. For example, the sensors 66, 68, 70, 72, 74 may include at least one of a Hall effect sensor, a giant magnetoresistance magnetometer, an AMR magnetometer, a magneto-optical sensor, a search coil magnetic field sensor, a magnetodiode, a fluxgate magnetometer, or any other sensor suitable to sense a magnetic field.

As shown in FIG. 1 , the sensors 66, 68, 70, 72, 74 may be coupled to a controller 78, which may calculate the magnitude of the applied torque 12 based on measures generated by the sensors 66, 68, 70, 72, 74. In some instances, the controller 78 and the torque sensor 10 may be separate components of a vehicular subsystem for determining the magnitude of the applied torque 12. In one such instance, the vehicular subsystem may be an electric power steering unit of a vehicle. Furthermore, it should be noted that the controller 78 may include any suitable logic, signal processing means, or components for enabling performance of the described functions. Additionally, it should be noted that, in other instances, the sensors 66, 68, 70, 72, 74 may be similarly configured to measure other forces applied to the shaft 14, such as stress and strain, and the controller 78 may be configured to determine a magnitude of such other forces.

FIG. 5A illustrates one instance of a method of calculating the magnitude of the applied torque 12. The method includes a step 80 of receiving the applied torque 12 with the shaft 14 of the torque sensor 10; a step 82 of generating a non-negligible magnetic field responsive to the applied torque 12 (e.g. the first or second magnetic field 50, 52) with a magnetoelastic region (e.g. the first or second magnetoelastic region 20, 22); a step 84 of generating a null region magnetic field measure corresponding to the magnitude of the ambient magnetic field 76 with each null region sensor (e.g. the first, second, and third null region sensors 70, 72, 74); a step 86 of generating a magnetoelastic region magnetic field measure corresponding to the magnitude of the ambient magnetic field 76 and the non-negligible magnetic field with a magnetoelastic region sensor (e.g. the first or second magnetoelastic region sensor 66, 68); and a step 88 of calculating the applied torque 12 based on the null region magnetic field measures and the magnetoelastic region magnetic field measure with the controller 78.

FIG. 5B further illustrates one instance of the step 88 of calculating the applied torque 12 with the controller 78. As shown, step 88 may include a step 90 of mapping the ambient magnetic field 76 based on the null region magnetic field measures, which may include a step 92 of calculating a line representing the magnitude of the ambient magnetic field with respect to distance along the shaft 14. Further, step 88 may include a step 94 of estimating the magnitude of the ambient magnetic field 76 at a distance of the magnetoelastic region sensor along the shaft 14 based on the line.

FIGS. 6A and 6B illustrate examples of step 90, 92, and 94 of step 88. In the instances of FIGS. 6A and 6B the controller 78 maps first, second, and third null region magnetic field measures 102, 104, 106 generated by the first, second, and third null region sensors 70, 72, 74, respectively. The first, second, and third null region magnetic field measures 102, 104, 106 are mapped according to the distance of the first, second, and third null region sensors 70, 72, 74 (i.e. −s₂, 0, and s₂, respectively) along the shaft 14 using closed circles “•”. In the instance of FIGS. 6A and 6B, −s₂=−2 cm, and s₂=2 cm. As previously stated, the null region magnetic field measures correspond to the magnitude of the ambient magnetic field 76. As such, the controller 78 maps the ambient magnetic field 76 by mapping the first, second, and third null region magnetic field measures 102, 104, 106. Further, the controller 78 calculates a line representing the magnitude of the ambient magnetic field 76 with respect to distance along the shaft 14. The controller 78 may then estimate the magnitude of the ambient magnetic field 76 at the distance of the magnetoelastic region sensor. In the instance of FIGS. 6A and 6B, the controller 78 estimates the magnitude of the ambient magnetic field 76 at −s₁=−1 cm and s₁=1 cm, the location of the first and second magnetoelastic region sensors 66, 68, respectively. The estimated magnitude of the ambient magnetic field 76 are represented using open circles “∘”.

FIG. 6A corresponds to the torque sensor 10 of FIG. 3 , which is disposed in the uniform ambient magnetic field 76. As shown in FIG. 6A, the first, second, and third null region magnetic field measures 102, 104, 106 equal 1 Gauss (G) and correspond to the magnitude of the uniform ambient magnetic field 76. As such, the controller 78 calculates a line using a constant function to represent the magnitude of the uniform ambient magnetic field with respect to distance along the shaft 14:

B _(a)(x)=1.

The controller 78 may estimate the magnitude of the ambient magnetic field 76 at −s₁=−1 cm and s₁=1 cm to be 1 G.

FIG. 6B corresponds to the torque sensor 10 of FIG. 4 , which is disposed in the non-uniform ambient magnetic field 76. As shown in FIG. 6B, the first, second, and third null region magnetic field measures 102, 104, 106 equal 1 G, 0.37 G, and 0.14 G, respectively, and correspond to the magnitude of the non-uniform ambient magnetic field 76. As such, the controller 78 calculates a line using an exponential function to represent the magnitude of the non-uniform ambient magnetic field with respect to distance along the shaft 14:

B _(a)(X)=e ^(−(0.5x+1)).

The controller 78 may estimate the magnitude of the ambient magnetic field 76 at −s₁=−1 cm and s₁=1 cm to be 0.61 G and 0.22 G, respectively.

In other instances, the controller 78 may estimate the magnitude of the ambient magnetic field 76 with respect to distance along the shaft 14 using a linear function, a power function, a root function, a polynomial function, a sinusoidal function, a rational function, and/or a logarithmic function. For example, a linear function may be represented as:

B _(a)(x)=Ax+B

The controller 78 may select values for “A” and “B” such that B_(a)(−s₂), B_(a)(0), and B_(a)(s₂) correspond to the null region magnetic field measures. As another example, a polynomial function may be represented as:

B _(a)(x)=A ₁ +A ₂ x+A ₃ x ² + . . . +A _(n) x ^(n-1).

The controller 78 may select a value for “n” based on desired precision of B_(a)(x). For instance, for more precise calculations of B_(a)(x), the controller 78 may select a greater value of n for a greater the number of exponentials in B_(a)(x). Furthermore, the controller 78 may select values for “A₁”, “A₂”, etc., such that such that B_(a)(−s₂), B_(a)(0), and B_(a)(s₂) correspond to the null region magnetic field measures. In some instances the controller 78 may calculate B_(a)(x) such that such that B_(a)(−s₂), B_(a)(0), and B_(a)(s₂) are within an adjustable or programmed tolerance of the null region magnetic field measures.

Also shown in FIG. 5B, step 88 may include a step 96 of determining the magnitude of the non-negligible magnetic field (e.g. the first magnetic field 50 and/or the second magnetic field 52) based on the estimated magnitude of the ambient magnetic field 76 and the magnetoelastic region magnetic field measure. As previously stated, the magnetoelastic region magnetic field measure corresponds to the magnitude of the ambient magnetic field 76 and the non-negligible magnetic field. For example, the magnetoelastic region magnetic field measure generated by the first magnetoelastic region sensor 66 corresponds to the magnitude of the ambient magnetic field 76 and the first magnetic field 50. As such, the controller 78 may determine the magnitude of the first magnetic field 50 by subtracting the estimated magnitude of the ambient magnetic field 76 from the magnetoelastic region magnetic field measure.

In the example of FIG. 6B, the controller 78 may determine the magnitude of the first magnetic field 50 by subtracting the estimated magnitude of the ambient magnetic field 76 at the location of the first magnetoelastic region sensor 66, B_(a)(−s₁), which is estimated to be 0.61 G, from the magnetoelastic region magnetic field measure generated by the first magnetoelastic region sensor 66. Similarly, the controller 78 may determine the magnitude of the second magnetic field 52 by subtracting the estimated magnitude of the ambient magnetic field 76 at the location of the second magnetoelastic region sensor 68, B_(a)(s₁), which is estimated to be 0.22 G, from the magnetoelastic region magnetic field measure generated by the second magnetoelastic region sensor 68.

Since the magnitude of applied torque 12 corresponds to a magnetic field generated by a magnetoelastic region of the shaft 14, the controller 78 may determine the magnitude of the applied torque 12 after determining the magnitude of the magnetic field. In some instances, the controller 78 may use a lookup table to determine the magnitude of the applied torque 12 based on the magnitude of the magnetic field. In instances where the torque sensor 10 includes multiple magnetoelastic regions, such as the instance of FIG. 1 , the controller 78 may average the magnitudes of the magnetic fields generated by the magnetoelastic regions of the shaft 14 and use a lookup table to determine the magnitude of the applied torque 12.

Advantageously, by calculating the applied torque 12 based on the null region magnetic field measures and the magnetoelastic region magnetic field measure, the torque sensor 10 is able to reject the ambient magnetic field 76. Further, by mapping the ambient magnetic field 76 using constant, linear, exponential, logarithmic, polynomic, sinusoidal, and a variety of other functions, the torque sensor 10 is able to approximate and reject uniform and non-uniform ambient magnetic fields.

In other instances, the torque sensor 10 may vary. For instance, the magnetoelastic regions of the torque sensor 10 may be magnetized to have different polarities. As an example, in FIG. 7A, the first magnetoelastic region 20 and the second magnetoelastic region 22 of the torque sensor 10 have opposing polarities.

In some instances, lengths of the null regions and the magnetoelastic regions may vary. For example, in FIG. 7B, the second null region 26 and the third null region 28 have a greater length than the second null region 26 and the third null region 28 in FIG. 1 . Additionally, the second magnetoelastic region 22 in FIG. 7B has a smaller length than the second magnetoelastic region 22 in FIG. 1 .

In some instances, the null regions and the magnetoelastic regions may be ordered along the shaft in any suitable fashion. For example, in FIG. 7C, the second null region 26 is disposed between the second magnetoelastic region 22 and the third null region 28.

In some instances, the torque sensor 10 may include any suitable number of magnetoelastic regions and null regions, and a corresponding number magnetoelastic region sensors and null region sensors. For example, in FIG. 7D, the torque sensor 10 includes one magnetoelastic region, the first magnetoelastic region 20, and one magnetoelastic region sensor, the first magnetoelastic region sensor 66. In FIG. 7E, the torque sensor 10 includes three magnetoelastic regions 20, 22, 108, three corresponding magnetoelastic regions sensors 66, 68, 112, four null regions 24, 26, 28, 110, and four corresponding null region sensors 70, 72, 74, 114.

In some instances, such as the instance of FIG. 7F, the torque sensor 10 may include fewer than three null regions. It has been contemplated that the torque sensor 10 may include one or more null regions and may therefore include fewer than three null regions. In such instances, while the torque sensor 10 includes fewer than three null regions, the torque sensor 10 may still include three or more null region sensors such that the controller 78 may calculate the line representing the magnitude of the ambient magnetic field with respect to distance along the shaft 14 using three null region magnetic field measures. For example, in FIG. 7F, the torque sensor 10 only includes the first null region 24, but the first, second, and third null region sensors 70, 72, 74 are disposed along the first null region 24 and generate a first, second, and third null region magnetic field measure. Generally, one or more null region sensors may be disposed proximal any null region.

It should be noted that, in the instances of the torque sensor 10 illustrated herein, the torque sensor 10 includes three or more null region sensors. It has been contemplated that the torque sensor 10 may include a fewer number of null region sensors. For example, in instances where the torque sensor 10 includes one null region sensor that generates a null region magnetic field measure, the controller 78 may calculate the line representing the magnitude of the ambient magnetic field with respect to distance along the shaft 14 by assuming a constant ambient magnetic field 76. As another example, in instances where the torque sensor 10 includes two null region sensors that generate (in total) two null region magnetic field measures, the controller 78 may calculate the line representing the magnitude of the ambient magnetic field with respect to distance along the shaft 14 by assuming a linear ambient magnetic field 76.

Several instances have been discussed in the foregoing description. However, the instances discussed herein are not intended to be exhaustive or limit the invention to any particular form. The terminology which has been used is intended to be in the nature of words of description rather than of limitation. Many modifications and variations are possible in light of the above teachings and the invention may be practiced otherwise than as specifically described. 

1. A torque sensor comprising: a shaft that receives an applied torque, the shaft comprising a magnetoelastic region that generates a non-negligible magnetic field responsive to the applied torque and one or more null regions that each generates a negligible magnetic field; a plurality of null region sensors, each null region sensor proximal one of the one or more null regions and generating a null region magnetic field measure corresponding to a magnitude of an ambient magnetic field; a magnetoelastic region sensor proximal the magnetoelastic region and generating a magnetoelastic region magnetic field measure corresponding to the magnitude of the ambient magnetic field and a magnitude of the non-negligible magnetic field; and a controller coupled to the plurality of null region sensors and the magnetoelastic region sensor that calculates a magnitude of the applied torque based on the null region magnetic field measures and the magnetoelastic region magnetic field measure.
 2. The torque sensor of claim 1, wherein the shaft receives the applied torque such that the magnetoelastic region generates the non-negligible magnetic field responsive to the applied torque, and wherein the controller calculates the magnitude of the applied torque by mapping the ambient magnetic field based on the null region magnetic field measures.
 3. The torque sensor of claim 2, wherein: each null region sensor is disposed at a distance along the shaft; the null region magnetic field measure generated by each null region sensor comprises a measure of the magnitude of the ambient magnetic field at the distance of the null region sensor along the shaft; and the controller maps the ambient magnetic field based on the null region magnetic field measures by calculating a line representing the magnitude of the ambient magnetic field with respect to distance along the shaft based on the null region magnetic field measures.
 4. The torque sensor of claim 3, wherein the line representing the magnitude of the ambient magnetic field with respect to distance along the shaft includes at least one of a constant function, a linear function, an exponential function, a power function, a root function, a polynomial function, a sinusoidal function, a rational function, or a logarithmic function.
 5. The torque sensor of claim 3, wherein: the magnetoelastic region sensor is disposed at a distance along the shaft; the magnetoelastic region magnetic field measure generated by the magnetoelastic region sensor is based on the magnitude of the ambient magnetic field at the distance of the magnetoelastic region sensor along the shaft and the magnitude of the non-negligible magnetic field; and the controller calculates the magnitude of the applied torque by: estimating, based on the line representing the magnitude of the ambient magnetic field with respect to distance along the shaft, the magnitude of the ambient magnetic field at the distance of the magnetoelastic region sensor along the shaft; determining the magnitude of the non-negligible magnetic field based on the estimated magnitude of the ambient magnetic field and the magnetoelastic region magnetic field measure; and determining the magnitude of the applied torque based on the magnitude of the non-negligible magnetic field.
 6. The torque sensor of claim 1, wherein the one or more null regions comprises a first null region, a second null region, and a third null region.
 7. The torque sensor of claim 6, wherein the plurality of null region sensors comprises: a first null region sensor disposed at a first distance along the shaft and proximal the first null region, the first null region generating a first null region magnetic field measure comprising a measure of the magnitude of the ambient magnetic field at the first distance; a second null region sensor disposed at a second distance along the shaft and proximal the second null region, the second null region sensor generating a second null region magnetic field measure comprising a measure of the magnitude of the ambient magnetic field at the second distance; and a third null region sensor disposed at a third distance along the shaft and proximal the third null region, the third null region sensor generating a third null region magnetic field measure comprising a measure of the magnitude of the ambient magnetic field at the third distance; and wherein the controller calculates the magnitude of the applied torque by mapping the ambient magnetic field based on the first null region magnetic field measure, the second null region magnetic field measure, and the third null region magnetic field measure by calculating a line representing the magnitude of the ambient magnetic field with respect to distance along the shaft based on the first null region magnetic field measure, the second null region magnetic field measure, and the third null region magnetic field measure.
 8. The torque sensor of claim 1, wherein: the shaft further comprises a second magnetoelastic region; the torque sensor further comprises a second magnetoelastic region sensor proximal the second magnetoelastic region that generates a second magnetoelastic region magnetic field measure; and the controller is coupled to magnetoelastic region sensor and the second magnetoelastic region sensor and calculates the magnitude of the applied torque based on the null region magnetic field measures, the magnetoelastic region magnetic field measure, and the second magnetoelastic region magnetic field measure.
 9. The torque sensor of claim 1, wherein the one or more null regions comprises a first null region, a second null region, and a third null region and the shaft comprises a second magnetoelastic region.
 10. The torque sensor of claim 9, wherein the shaft comprises a first end and an opposing second end and an axis defined between the first and second ends.
 11. The torque sensor of claim 10, wherein the applied torque is applied to the shaft of the torque sensor about the axis.
 12. The torque sensor of claim 10, wherein the first null region, the second null region, the third null region, the magnetoelastic region, and the second magnetoelastic region each comprises a first end and an opposing second end defining a length along the axis.
 13. The torque sensor of claim 12, wherein the magnetoelastic region is disposed between the first null region and the second null region such that the first end of the magnetoelastic region contacts the second end of the first null region and the second end of the magnetoelastic region contacts the first end of the second null region; and wherein the second magnetoelastic region is disposed between the second null region and the third null region such that the first end of the second magnetoelastic region contacts the second end of the second null region and the second end of the second magnetoelastic region contacts the first end of the third null region.
 14. The torque sensor of claim 1, wherein the plurality of null region sensors and the magnetoelastic region sensor are disposed on a housing spaced from and adjacent to the shaft.
 15. The torque sensor of claim 1, wherein the plurality of null region sensors and the magnetoelastic region sensor each comprises at least one of a Hall effect sensor, a giant magnetoresistance magnetometer, an AMR magnetometer, a magneto-optical sensor, a search coil magnetic field sensor, a magnetodiode, or a fluxgate magnetometer.
 16. A torque sensor comprising: a shaft that receives an applied torque, the shaft comprising: a first null region, a second null region, and a third null region that each generates a negligible magnetic field; and a first magnetoelastic region and a second magnetoelastic region that each generates a non-negligible magnetic field responsive to the applied torque; a first null region sensor proximal the first null region and generating a first null region magnetic field measure corresponding to a magnitude of an ambient magnetic field; a second null region sensor proximal the second null region and generating a second null region magnetic field measure corresponding to the magnitude of the ambient magnetic field; a third null region sensor proximal the third null region and generating a third null region magnetic field measure corresponding to the magnitude of the ambient magnetic field; a first magnetoelastic region sensor proximal the first magnetoelastic region and generating a first magnetoelastic region magnetic field measure corresponding to the magnitude of the ambient magnetic field and a magnitude of the non-negligible magnetic field generated by the first magnetoelastic region responsive to the applied torque; a second magnetoelastic region sensor proximal the second magnetoelastic region and generating a second magnetoelastic region magnetic field measure corresponding to the magnitude of the ambient magnetic field and a magnitude of the non-negligible magnetic field generated by the second magnetoelastic region responsive to the applied torque; and a controller coupled to the first null region sensor, the second null region sensor, the third null region sensor, the first magnetoelastic region sensor, and the second magnetoelastic region sensor that calculates a magnitude of the applied torque based on the first null region magnetic field measure, the second null region magnetic field measure, the third null region magnetic field measure, the first magnetoelastic region magnetic field measure, and the second magnetoelastic region magnetic field measure.
 17. A method of calculating a magnitude of an applied torque using a torque sensor, the torque sensor including a shaft that includes a plurality of null regions that each generates a negligible magnetic field and a magnetoelastic region that generates a non-negligible magnetic field responsive to the applied torque, a plurality of null region sensors each proximal one of the null regions, a magnetoelastic region sensor proximal the magnetoelastic region, and a controller coupled to the plurality of null region sensors and the magnetoelastic region sensor, the method comprising steps of: receiving, with the shaft, the applied torque; generating, with the magnetoelastic region, the non-negligible magnetic field responsive to the applied torque; generating, with each null region sensor, a null region magnetic field measure corresponding to an ambient magnetic field; generating, with the magnetoelastic region sensor, a magnetoelastic region magnetic field measure corresponding to the ambient magnetic field and the non-negligible magnetic field; and calculating, with the controller, the magnitude of the applied torque based on the null region magnetic field measures and the magnetoelastic region magnetic field measure.
 18. The method of claim 17, wherein the step of calculating the magnitude of the applied torque comprises a step of mapping, with the controller, the ambient magnetic field based on the null region magnetic field measures.
 19. The method of claim 18, wherein each null region sensor is disposed at a distance along the shaft and the null region magnetic field measure generated by each null region sensor includes a measure of the magnitude of the ambient magnetic field at the distance of the null region sensor along the shaft, and wherein the step of mapping the ambient magnetic field comprises a step of calculating, with the controller, a line representing the magnitude of the ambient magnetic field with respect to distance along the shaft.
 20. The method of claim 19, wherein the magnetoelastic region sensor is disposed at a distance along the shaft and the magnetoelastic region magnetic field measure generated by the magnetoelastic region sensor is based on a measure of the magnitude of the ambient magnetic field at the distance of the magnetoelastic region sensor along the shaft and a measure of a magnitude of the non-negligible magnetic field, wherein the step of calculating the magnitude of the applied torque comprises steps of: estimating, with the controller, the magnitude of the ambient magnetic field at the distance of the magnetoelastic region sensor along the shaft based on the line representing the magnitude of the ambient magnetic field with respect to distance along the shaft; determining, with the controller, the magnitude of the non-negligible magnetic field based on the estimated magnitude of the ambient magnetic field and the magnetoelastic region magnetic field measure; and determining, with the controller, the magnitude of the applied torque based on the magnitude of the non-negligible magnetic field. 